how to get Quicklook to load image at index when selected in uicollectionview

Question

i got a uicollectionsview

when i select i image from there i want it to show in the Quicklook i think i got it to select the file prober but showing it crashes the app with this message :

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSURL length]: unrecognized selector sent to instance 0xb7be9c0'

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(@"didselect");
QLPreviewController * preview = [[QLPreviewController alloc] init];
preview.dataSource = self;
preview.currentPreviewItemIndex = indexPath.row;
[self presentViewController:preview animated:YES completion:Nil];
}

#pragma mark -
#pragma mark QLPreviewControllerDelegate methods


- (BOOL)previewController:(QLPreviewController *)controller shouldOpenURL:(NSURL *)url forPreviewItem:(id <QLPreviewItem>)item {

return YES;
}


#pragma mark -
#pragma mark QLPreviewControllerDataSource methods
- (NSInteger) numberOfPreviewItemsInPreviewController: (QLPreviewController *) controller {

return [photoURLsLargeImage count];
}

this is where my problem is, i think:

- (id <QLPreviewItem>) previewController: (QLPreviewController *) controller previewItemAtIndex: (NSInteger) index {
NSString *entry = [photoURLsLargeImage objectAtIndex:index];
return [NSURL fileURLWithPath:entry];
}

photoURLsLargeImage is a nsmutablearray with at least 17 objects fetched from flickr

Answer 1

Add datasource

preview.dataSource = self;

And add the delegate method.

- (NSInteger)numberOfPreviewItemsInPreviewController:(QLPreviewController *)controller
{    
return 1;
}

Your problem solved.

Answer 2

You should use this currentPreviewItemIndex:

The index, within the preview item navigation list, of the item currently displayed in the Quick Look preview controller. You can change which item is displayed, among those in a navigation list, by setting this property’s value. If no item is being displayed, this property’s value is NSNotFound.

Apple Doc